Gas-filled arc discharge lamps are used as ambient room lighting devices, indicators, neon signs, tanning bulbs, photographic electronic flashes and A/V projector devices. Because gas discharge lamps generally last longer than conventional incandescent lamps and can generate ultraviolet light, they are particularly well-suited for industrial use, such as for spectroscopy and materials analysis. In industrial settings it is desirable for these lamps to operate for at least 2000 hours while maintaining their light output intensity level at a minimum of 50% of their initial intensity.
Examples of typical gas discharge lamps include U.S. Pat. Nos. 4,366,408; 5,522,669; 5,864,209; 5,972,469; and 6,078,132, all of which are hereby incorporated by reference in their entirety. Some gas discharge lamps cannot satisfy the above-noted industrial performance requirements. A gas discharge lamp, frequently referred to as a Long Life (“LL”) lamp, has been successfully designed to satisfy at least some of these requirements. While these LL lamps often perform well enough to meet the performance requirements, their design has given rise to other problems, such as short circuits occurring because of an accumulation of deposited conductive material caused by sputtering in the light emitting portion, undesirable arcing, “noisy” or unstable light output and poor overall structural integrity.
Referring to FIGS. 1-2, an exemplary light emitting portion 10 of a conventional arc gas discharge lamp is shown. The light emitting portion 10 includes an anode 12, focusing electrode or baffle 14, an insulator 16 arranged within an opening 18 of a support 19, all of which are oriented towards a cathode filament 20 and encased within a first cover 22 and a second cover 24. As shown in FIG. 2, conductive material 26 accumulates on the interior surface of the cavity 28 in the insulator 16 as a result of sputtering caused by repeatedly striking the anode 12 with thermoelectrons. This accumulation of material 26 forms a conductive path between the anode 12 and the baffle 14 leading to short circuiting and the other undesirable effects mentioned above.